I have a humminbird 998 SI. I usually use the map feature on there when it is foggy to stay in the channel. It use to have several different screens with map views. For some reason when I tried to use it the other morning all of the map pages were blank and when I pressed the go to button I think it was it said (No GPS Fix) what would cause it to no longer show the mapping but it still shows the Side imaging and everything else. It shows the on screen display for depth and tempature but also no longer shows the speed. I am assuming the depth finder itself is working fine but the gps part is messed up. Any suggestions?